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Laser zooms in on tiny molecules

A new laser-powered spectrometer will allow scientists to study tiny moving molecules at very high resolution.

The team that developed the amped-up electron paramagnetic resonance (EPR) spectrometer has used it to study the electron spin of free radicals and nitrogen atoms trapped inside a diamond. A paper describing the work appears in Nature.

“We developed the world’s first free-electron laser-powered EPR spectrometer,” says Susumu Takahashi, assistant professor of chemistry at the University of Southern California (USC) and the paper’s lead author.

“This ultra high-frequency, high-power EPR system gives us extremely good time resolution. For example, it enables us to film biological molecules in motion.”

By using a high-powered laser, the researchers were able to significantly enhance EPR spectroscopy, which uses electromagnetic radiation and magnetic fields to excite electrons. These excited electrons emit electromagnetic radiation that reveals details about the structure of the targeted molecules.

EPR spectroscopy has existed for decades. Its limiting factor is the electromagnetic radiation source used to excite the electrons—it becomes more powerful at high magnetic fields and frequencies, and, when targeted, electrons are excited with pulses of power as opposed to continuous waves.

Until now, scientists performed pulsed EPR spectroscopy with a few tens of GHz of electromagnetic radiation. Using the free electron laser (FEL) at the University of California, Santa Barbara—which emits a pulsed beam of electromagnetic radiation—the team was able to use 240 GHz of electromagnetic radiation to power an EPR spectrometer.

“Each electron can be thought of as a tiny magnet that senses the magnetic fields caused by atoms in its nano-neighborhood,” says Mark Sherwin, professor of physics and director of the Institute for Terahertz Science and Technology at UC Santa Barbara.

“With FEL-powered EPR, we have shattered the electromagnetic bottleneck that EPR has faced, enabling electrons to report on faster motions occurring over longer distances than ever before.

“We look forward to breakthrough science that will lay foundations for discoveries like new drugs and more efficient plastic solar cells.”